As shown in FIGS. 1 and 2 in a prior art method a flat ring blank 2 is produced by punching a rectangular metal sheet 1 by a press. Then a part 3 formed with an opening 7 is produced by stretching the flange inwardly of the ring material 2 as indicated at 3a and shrink flanging outwardly thereof as indicated at 3b by a press.
In the method of production of the prior art, portions of the material or rectangular metal material 1 corresponding to four corners 4 and a portion 5 corresponding to the opening 7 are scrapped as waste material. Thus, the material has a very low yield and a large portion thereof is discarded as waste material. When the part 3 is formed by drawing, the stretch flange 3a has its thickness reduced in going from its base toward its end, thereby causing a reduction in strength. Meanwhile the shrink flange 3b has its thickness increased in going from its base toward its end, thereby causing an increase in weight.